An arrangement of the type mentioned in the introduction has been disclosed by French Patent Specification 1,118,857. This known arrangement comprises two compression bars 2 which can be displaced with respect to one another counter to the force of a compression spring 7 (see, in particular, FIGS. 5-7). The prestressing of the spring can be changed by an adjustment device provided with a manipulation means 17, as a result of which the bending properties of the ski are changed. In all the embodiments, as is disclosed by FIG. 3 of this document with reference to page 3, left-hand column, first full paragraph, use is made exclusively of compression springs, the ski also being subjected exclusively to compressive loading. Subjecting the ski to tensile loading, as is illustrated in FIGS. 10 and 11 of the French patent specification, would require a corresponding configuration of the springs 5, as is described on page 4, left-hand column, following lines 44. Such a configuration, however, is not disclosed in French Patent Specification 1,118,857. The measure of permitting tensile forces to be exerted on the ski according to FIG. 2 of this French patent specification was, in accordance with the description on page 2, right-hand column, following the third line from the end, the subject matter of an earlier application (French Patent Specification 1,109,560 by the same inventor).
As has already been outlined, compression springs are exclusively illustrated and described in the more recent French Patent Specification (1,118,857). The previously mentioned sentence concerning the fact that one would have to configure the springs correspondingly in order to achieve transmission of tension can be best understood in conjunction with the solution described above and contained in the earlier French patent specification mentioned in the more recent French patent specification. For this purpose, one of the spring systems, for the sake of simplicity this being the spring system according to FIG. 9, would have to be used instead of the cable lines (2 and 3), it being the case that transmission of tension could also then take place by adjustment of the screw 4 by means of the compression bars and/or screw-bolts. It would, however, be necessary for this purpose to retain the entire control system according to FIG. 2 of French Patent Specification 1,109,560 and, in addition, to install a spring system according to FIG. 9 on both sides. This would mean that a total of three manipulation means would have to be actuated, namely the adjustment screw 4 and each cylinder 27. Correspondingly, with the installation of a spring system according to FIG. 6 or FIG. 8, in each case one manipulation means 17 would be additionally required.
Moreover, French Patent Specification 1,118,857 describes a stiffening device with a compression bar located on the upper side of the ski, the adjustment spindle being represented as being located spatially above or beneath the upper side of the ski. The configuration of the compression bar as a rack element, just as a sunken configuration and the articulation of the racks, results in a considerable degree of manufacturing expenditure.
Another arrangement is disclosed in German Patent Specification 1,298,024, in accordance with which a camactuated adjustment system makes it possible to change the hardness of the ski via push rods. The push rods are fitted beneath the upper side of the ski and they are set by means of cams or threaded spindles. On account of the discontinuous cam curvature, the setting force is greater than the fixing force when the adjustment system is actuated, this resulting in an additional exertion of force being necessary. Furthermore, the installation of said known arrangement in the body of the ski is a laborious task and can only be carried out in the factory.
Precurved bars are described in U.S. Pat. No. 4,221,400. Said bars are fitted in cylindrical bores which run within the ski, along the direction of the longitudinal axis. These bars are rotated in order to change the curvature, hardness and rigidity of the ski. The simultaneous actuation of a plurality of bars involves a high degree of outlay, added to which is the fact that there is a considerable exertion of force.
U.S. Pat. No. 4,300,786 discloses exchangeable stiffening bars which are fitted on the sides of the ski and influence the flexibility of the ski as desired. However, exchanging the bars may itself be regarded as problematical because a multiplicity of stiffening bars have to be carried along for the various skiing/snow boarding conditions.
German Offenlegungsschrift 3,315,638 describes a stiffening device with a tension band which runs essentially parallel to the upper side of the ski, the stiffening forces being introduced into the ski by the tension band via vertically arranged adjustment devices.
French Offenlegungsschrift 2,448,360 specifies a system which is similar to this. Here, there is provided in the front region of the ski a stiffening device which is elevated in the vertical direction and can involve performance-related risks and problems with dirt build-up in the stiffening device.
In U.S. Pat. No. 2,258,046, a divided stiffening band is actuated by a horizontally mounted circular eccentric body. Actuation takes place via a lever, by means of a boot. This configuration gives some protection against the ingress of snow, whereas the introduction of force into the ski requires two additional plate-like parts.
A further known technical solution is specified in French Patent Specification 2,689,411, in the case of which a two-part stiffening body which is divided in its center and is connected elastically or rigidly to the upper side of the ski is provided. Here, in order to change the hardness and rigidity of the ski, use is made of the type of gap formation between the front and rear parts of the stiffening body. The insertion of elastic elements into the gap achieves stepped bending characteristics in one direction, but it is not possible for the user to change the rigidity of the ski voluntarily.
French Patent Specification 2,690,078 strengthens the ski dynamically in one direction during travel by means of a toggle lever and by way of the heel pressure, exerted by the rear part of the ski boot, which acts on the stiffening device. German Utility Model 91 16 875.9 describes a bearing-plate arrangement in the case of which the bearing plate is stiffened by a cam plate or a centrifugal weight. WO94/08669 discloses a stiffening bar which is fitted in an elevated manner against the upper side of the ski and permits continuous adjustment via a threaded adjustment disk.
French Patent Specification 2,649,902 discloses a stiffenable bearing plate which is fitted in an elevated manner with respect to the upper side of the ski, is mounted elastically in the direction of the axis of the ski and is intended for a complete safety binding.
In the number of solutions outlined above, additional appliances (levers or similar small tools) are required for adjustment purposes, and carrying these additional appliances along during travel is both obstructive and seems questionable from a safety point of view. In addition, in certain embodiments, there is still the possibility of icing up, this resulting in the actual function of the adjustment means being restricted. Likewise, it is not possible, in all solutions, to change the level of convexity to a sufficient degree.